Impact of Wet-Dry Cycling on the Phase Behavior and Compartmentalization Properties of Complex Coacervates

Wet-dry cycling on the early Earth is thought to have facilitated production of molecular building blocks of life, but thus far its impact on self-assembly and compartmentalization of resulting (macro)molecules has been limited. We investigated dehydration/rehydration of complex coacervates, which are membraneless compartments formed by phase separation of polyelectrolyte solutions, and suggested as protocell models. Depending on initial composition of a poly(diallyldimethylammonium)/poly(acrylic acid) system, drying enabled formation or disassembly of coacervate droplets. In compartments surviving tenfold dehydration, partitioning of a fluorescent RNA oligonucleotide decreased, while its local concentration inside the coacervates remained nearly constant, despite increasing tenfold globally. RNA mobility was also enhanced as the system dehydrated. These changes can be understood as resulting from drying induced compositional movements on the phase diagram, with increased ionic strength being particularly important in determining coacervate properties. These results showed that wet-dry cycling can alter the phase behavior and protocell-relevant functions of complex coacervates.